The kidney is an important organ that functions to maintain good physical health through filtrating and removing toxic substances and waste products generated by metabolic activity in the body from the blood. Renal failure is a serious disease that impairs the function of the kidney, but since no effective drug therapy for this disease has yet been established, this disease is at present treated by renal transplantation, dialysis or the like. However, renal transplantation is faced with the problem of severe lack of donor organs, and dialysis also has the problems of the onset of complications and a heavy burden of medical costs; thus, there is a desire to develop a new therapy for this disease.
Meanwhile, there have already been reports on pluripotent cells, such as embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs) obtained by introducing a reprogramming factor(s) into somatic cells (PTLs 1 and 2). Various studies have now been conducted to develop a new therapy for renal failure which involves transplantation of renal cells obtained by inducing differentiation of such PSCs. Another focus has been placed on developing a therapeutic drug for renal failure using homogeneous renal cells derived from such PSCs.
It is known that mammalian kidneys develop through the three stages of pronephros, mesonephros and metanephros, and that among them, the metanephros develops in the posterior region of intermediate mesoderm. In previous researches, a method for inducing differentiation of mouse PSCs into intermediate mesoderm was studied (NPL 1), and Odd-Skipped Related Transcription Factor 1 (OSR1) was identified as a characteristic marker of intermediate mesoderm. Also, SIX Homeobox 2 (SIX2) is known as one of factors characterizing RPCs (NPLs 2 and 3). As a result of the study with the human iPSCs (OSR1-GFP reporter human iPS cells) generated by introducing the green fluorescent protein (GFP) gene using a bacterial artificial chromosome (BAC) vector through homologous recombination with endogenous OSR1 allele, human PSCs were successfully induced to differentiate into intermediate mesoderm using Activin A, Wnt protein, bone morphogenetic protein (BMP) and various low-molecular compounds (NPL 3, PTL 3). Then, as a result of the study with OSR1-GFP & SIX2-tdTomato reporter human iPS cell lines generated by introducing the red fluorescent protein, tdTomato, into SIX2 loci in the OSR1-GFP reporter human iPS cell lines using the same homologous recombination procedure as adopted by Mae, et al. (NPL 3), a system for inducing differentiation of human PSCs into RPCs was successfully constructed, and the therapeutic efficacy of a therapy with the thus-obtained RPCs was confirmed in acute kidney injury models (NPL 4, PTL 4).